Development of Catalysts for Polymer Degradation and Their Application to Plastics Recycling and Hydrogen Production

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H-gallosilicate, gallium oxide supported on FSM-16, and H-borosilicate have been developed as catalysts for chemical recycling of polyolefins by degradation into useful petrochemical feedstocks.The gallosilicate showed a high activity for the coproduction of hydrogen and aromatic hydrocarbons, mostly benzene, toluene, and xylenes (BTX), from the degradation of low- and high-density polyethylene and polypropylene. The hydrogen and BTX yields increased with reaction temperature and went up to over 3 and 55 wt% at 500 ℃, respectively. The product distribution was influenced little by the structure of the polyolefins to be degraded. This can be explained by a mechanism involving frequent skeletal isomerization of the decomposed fragments.A high hydrogen yield of 4.5 wt%, the value of which corresponds to 32 % of the moles of hydrogen being contained in the polyolefins, was obtained when Ga/FSM-16 was used as a catalyst, although the yield of aromatics was reduced because of their transformation into carbonaceous materials on the catalyst surface.H-borosilicate was found to be a catalyst that can break down polyolefins into lower molecular weight olefins. Propylene and butenes were the main products and their yields increased with reaction temperature, while paraffins and aromatics were obtained in limited amounts. Almost the same product distributions were observed from the degradation of the three polyolefins.These results indicate that the developed technologies using gallium and boron catalysts are highly promising as new options for chemical recycling of polyolefins.